This invention relates to the magnetic navigation of medical devices, and in particular to magnetic medical devices with changeable magnetic moments, and to methods of navigating magnetic medical devices with changeable magnetic moments.
It has long been proposed to magnetically navigate catheters through the body with an externally applied magnetic field. Recent advances have made the magnetic navigation of catheters and other medical devices practical. Typically, the medical device is provided with a permanent or a permeable magnetic element. An external source magnet, which may be a permanent magnet, an electromagnet, or a superconducting electromagnet, is used to apply a magnetic field and/or gradient to an operating region inside a patient to act on the magnetic element in the medical device to orient and/or move the medical device in the operating region. The medical device is oriented and/or moved by changing the magnetic field and/or gradient applied by the external source magnet.
In the case of stationary electromagnetic and superconducting electromagnetic source magnets, changing the magnetic field and/or gradient is accomplished by changing the currents supplied to the source magnet. In the case of moveable source magnets, changing the magnetic field and/or gradient is accomplished by changing the position and/or orientation of the source magnet. If the moveable source magnet is an electromagnet or a superconducting electromagnet, the magnetic field and/or gradient can also be changed by changing the current supplied to the magnet.
While systems with stationary electromagnets and superconducting electromagnets provide fast, safe, and effective navigation of medical devices, it can be expensive to construct and maintain a system that operates in real time to provide unrestricted navigation in the body. Similarly while systems with moving source magnets provide fast, safe, and effective navigation of medical devices, it can be expensive to construct and maintain a system that can accurately move the source magnets to make a selected change in the magnet field and/or gradient.
The changing fields and gradients created by the source magnets are strong and will usually require shielding at many health care facilities. This shielding is another difficulty and expense of magnetic navigation systems that employ changing source magnetic fields and gradients to navigate magnetic medical devices in the body.
While systems using changing source magnet magnetic fields and gradients provide precise control and a high degree of navigational flexibility, for some types of medical procedures a less complicated, less expensive, and preferably more compact navigation system would be desirable.
Generally according to the principles of the present invention a magnetic medical device having a changeable magnetic moment is introduced into an operating region in the body, a navigating magnetic field is applied to the operating region, and the magnetic moment of the magnetic medical device is changed to orient the magnetic medical device relative to the externally applied navigating magnetic field.
As used herein a magnetic medical device having a changeable magnetic moment does not include magnetic medical devices that have a permeable magnetic material in which a magnetic moment is induced in the permeable magnetic material by the application of the navigating magnetic field, but only to magnetic medical devices in which the change in the magnetic moment direction is independent from the navigating magnetic field, and the magnetic moment is acted upon by the navigating magnetic field.
According to the first embodiment of the invention, the magnetic medical device includes at least one electromagnetic coil, and preferable more than one coil, so that the magnetic moment of the medical device can be changed by changing the current in the at least one electromagnetic coil. This causes the magnetic medical device to move with respect to the externally applied navigating magnetic field.
According to a second embodiment, the magnetic medical device includes a moveable permanent magnet, movement of which causes the magnetic moment of the medical device to change. In a first construction or this second embodiment, the permanent magnet is moved with a mechanism. In a second construction of this second embodiment, the permanent magnet is moved with one or more electromagnetic coils that selectively create a local magnetic field to orient the permanent magnet to change the magnetic moment of the magnetic medical device. A lock can be provided to selectively lock the permanent magnet in its selected position.
According to a third embodiment, the magnetic medical device includes a moveable permanent magnet, movement of which causes the magnetic moment of the medical device to change. The permanent magnet is lockable in the magnetic medical device, so that its orientation remains fixed relative to the magnetic medical device. The orientation of the permanent magnet relative to the magnetic medical device can be changed by unlocking the permanent magnet, applying an external configuring magnetic field to change the orientation of the permanent magnet, and locking the permanent magnet. The external configuring magnetic field can then be removed, and an external navigating magnet field applied to orient the magnetic medical device with its new magnetic moment.